Analyte sensor

ABSTRACT

Sensors and methods for measurement of an analyte in a medium within a living animal are described. The sensor may include an inductive element that may receive power from an external device. The sensor may also include a charge storage device (CSD) and a memory. The sensor may perform analyte measurements initiated by the external device using power received from the external device and convey the analyte measurements to the external device using the inductive element. The sensor also may perform autonomous analyte measurements using the on board charge device&#39;s power and store the autonomous analyte measurements in the memory. The sensor may convey one or more stored analyte measurements to the external device using the inductive element using power received from the external device. The sensor may include a CSD-powered clock and a CSD-powered measurement scheduler that initiate the autonomous analyte measurements.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 14/629,943, filed on Feb. 24, 2015, which is incorporated byreference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to a sensor for obtaining analytemeasurements. Specifically, the present invention relates to animplantable sensor and methods of using the same that improve analytesensor measurement.

Discussion of the Background

An implantable sensor that has no charge storage device may relyexclusively on an external device for operational power (e.g., tooperate its circuitry for making measurements and conveying the data tothe external device). The sensor and the external device may eachinclude an inductive element (e.g., coil). The sensor may receive powerfrom the external device when the external device uses its inductiveelement to generate an electrodynamic field and the inductive elementsof the sensor and external device are magnetically coupled within theelectrodynamic field. However, with no internal power source, the sensoris dormant if the sensor is not located in the proximity of the externaldevice (i.e., if the inductive elements of the sensor and the externaldevice are not coupled within the electrodynamic field generated by theexternal device).

For instance, the sensor having no charge storage device may beimplanted in the arm of a human patient, and the sensor may be locatedin the proximity of the external device when the human patient wears anarmband having the external device therein. The sensor would be able totake analyte measurements and convey data to the external device whilethe patient is wearing the armband, but the sensor would not be able toable to take analyte measurements while the patient was not wearing thearmband (e.g., because the human patient is swimming or showering), andthe result would be a gap in analyte measurement information.

Accordingly, there is a need for an improved sensor and methods forusing the same that improve the ability of the sensor to take analytemeasurements.

SUMMARY

One aspect of the invention may provide a sensor for implantation withina living animal and measurement of an analyte in a medium within theliving animal. The sensor may include an analyte indicator, sensorelements, an inductive element, an input/output circuit, a measurementcontroller, and a charge storage device. The analyte indicator may beconfigured to exhibit a detectable property based on the amount orconcentration of the analyte in the medium. The sensor elements may beconfigured to generate an analyte measurement signal based on thedetectable property exhibited by the analyte indicator. The inductiveelement may be configured to produce a current when in an electrodynamicfield generated by an external device. The input/output circuit may beconfigured to wirelessly convey measurement information to the externaldevice via the inductive element. The measurement controller may beconfigured to (i) control the sensor elements to generate a firstanalyte measurement signal using power provided by the charge storagedevice while the inductive element is not in an electrodynamic fieldgenerated by the external device; (ii) generate first measurementinformation based on the first analyte measurement signal; and (iii)control the input/output circuit to wirelessly convey the firstmeasurement information to the external device while the inductiveelement is in an electrodynamic field generated by the external device.

In some embodiments, the sensor may include a nonvolatile storagemedium. In some embodiments, the measurement controller may be furtherconfigured to store the first measurement information in the nonvolatilestorage medium. In some embodiments, the measurement controller may befurther configured to: control the sensor elements to generate a secondanalyte measurement signal using the power provided by the chargestorage device while the inductive element is not in an electrodynamicfield generated by the external device; generate second measurementinformation based on the second analyte measurement signal; store thesecond measurement information in the nonvolatile storage medium; andcontrol the input/output circuit to wirelessly convey the secondmeasurement information to the external device while the inductiveelement is in an electrodynamic field generated by the external device.

In some embodiments, the measurement controller may be furtherconfigured to: control the sensor elements to generate a second analytemeasurement signal while the inductive element is in an electrodynamicfield generated by the external device; generate second measurementinformation based on the second analyte measurement signal; and controlthe input/output circuit to wirelessly convey the second measurementinformation to the external device while the inductive element is in anelectrodynamic field generated by the external device.

In some embodiments, the sensor may include a clock that is powered bythe charge storage device. In some embodiments, the clock may be alow-power oscillator, real time clock. In some embodiments, the sensormay include a measurement scheduler that is powered by the chargestorage device and configured to issue a first autonomous measurementcommand based on an output of the clock, and the measurement controllermay be configured to control the sensor elements to generate the firstanalyte measurement signal in response to the first autonomousmeasurement command. In some embodiments, the measurement scheduler maybe configured to issue autonomous measurement commands at periodicintervals based on the output of the clock. In some embodiments, thesensor may include a power switch configured to switch one or more ofthe sensor elements, the input/output circuit, and the measurementcontroller from being powered by externally supplied power to beingpowered by the charge storage device in response to the first autonomousmeasurement command.

In some embodiments, the input/output circuit may include: a capacitor;and a tuning capacitor bank configured to dynamically tune an LC tankcircuit comprising the inductive element and the capacitor and to changea resonant frequency of the LC tank circuit. In some embodiments, thetuning capacitor bank may include a varactor diode. In some embodiments,the input/output circuit may include an over-temperature protectioncircuit configured to control the tuning capacitor bank to detune the LCtank circuit so as to reduce power delivered by the LC tank circuit inthe case of overheating of the sensor.

In some embodiments, the detectable property exhibited by the analyteindicator may be an optical characteristic responsive to the amount orconcentration of the analyte in the medium, and the sensor elements mayinclude: a first photodetector configured to output an analog lightmeasurement signal indicative of the amount of light received by thefirst photodetector; and a first light source configured to emit firstexcitation light to the analyte indicator. In some embodiments, thesensor elements may further include a second light source configured toemit second excitation light to the analyte indicator, and the first andsecond excitation lights may have different wavelengths. In someembodiments, the sensor elements may further include a secondphotodetector configured to output an analog light measurement signalindicative of the amount of light received by the second photodetector.In some embodiments, the sensor may include: a first optical filterconfigured to cover a photosensitive side of the first photodetector andto allow light having a first wavelength to pass through; and a secondoptical filter configured to cover a photosensitive side of the secondphotodetector and to allow light having a second wavelength to passthrough, and the first and second wavelengths may be different. In someembodiments, the first and second optical filters may be coated on thephotosensitive sides of the first and second photodetectors,respectively. In some embodiments, the sensor may include asemiconductor substrate, and the first photodetector may be fabricatedin the semiconductor substrate.

In some embodiments, the input/output circuit may include: a rectifierconfigured to convert an alternating current produced by the inductiveelement while the inductive element is in an electrodynamic fieldgenerated by the external device to a direct current; and a chargerconfigured to recharge the charge storage device using the directcurrent generated by the rectifier. In some embodiments, the sensorelements may include: photodetectors symmetrically arranged on eitherside of a center line running between the photodetectors; and lightsources having emission points on the center line. In some embodiments,the first measurement information may include a time-stamp identifyingthe time at which the first measurement information was generated. Insome embodiments, the sensor may include an analog to digital converter(ADC) configured to convert an analog analyte measurement signal to adigital analyte measurement signal.

In some embodiments, the sensor elements may include: a firsttemperature transducer configured to output a first analog temperaturemeasurement signal indicative of a temperature of the sensor; and asecond temperature transducer configured to output a second analogtemperature measurement signal indicative of the temperature of thesensor. In some embodiments, the inductive element may be a coil. Insome embodiments, the charge storage device and semiconductor substratemay be located within the coil.

In some embodiments, the medium may be interstitial, intravascular, orintraperitoneal fluid. In some embodiments, the analyte may be glucose.In some embodiments, the input/output circuit may include a monitorconfigured to detect whether the voltage of the charge storage device isabove or below a threshold.

Another aspect of the invention may provide a method of using a sensorto measure an analyte in a medium within a living animal. The method mayinclude controlling the sensor elements of the sensor to generate afirst analyte measurement signal using power provided by a chargestorage device of the sensor while an inductive element of the sensor isnot in an electrodynamic field generated by an external device. Thesensor elements may be configured to generate the first analytemeasurement signal based on a detectable property exhibited by ananalyte indicator of the sensor, and the analyte indicator may beconfigured to exhibit the detectable property based on the amount orconcentration of the analyte in the medium. The method may includegenerating first measurement information based on the first analytemeasurement signal. The method may include controlling an input/outputcircuit of the sensor to wirelessly convey the first measurementinformation to the external device via the inductive element while theinductive element is in an electrodynamic field generated by theexternal device.

In some embodiments, method may include: storing the first measurementinformation in a nonvolatile storage medium of the sensor; controllingthe sensor elements to generate a second analyte measurement signalusing power provided by the charge storage device while the inductiveelement is not in an electrodynamic field generated by the externaldevice; generating second measurement information based on the secondanalyte measurement signal; and controlling the input/output circuit ofthe sensor to wirelessly convey the stored second measurementinformation to the external device via the inductive element while theinductive element is in an electrodynamic field generated by theexternal device. In some embodiments, the method may include: issuing anautonomous measurement command based on the output of a clock that ispowered by the charge storage device; and switching the sensor elementsfrom being powered by externally supplied power to being powered by thecharge storage device in response to the autonomous measurement command.

Another aspect of the invention may provide a sensor for implantationwithin a living animal and measurement of an analyte in a medium withinthe living animal. The sensor may include: an analyte indicator, sensorelements, a measurement controller, a non-volatile storage medium, acharge storage device, and a measurement scheduler. The analyteindicator may be configured to exhibit a detectable property based onthe amount or concentration of the analyte in the medium. The sensorelements may be configured to generate an analyte measurement signalbased on the detectable property exhibited by the analyte indicator. Themeasurement scheduler may be powered by the charge storage device and isconfigured to issue an autonomous measurement command. The measurementcontroller may be configured to: (i) control the sensor elements togenerate a first analyte measurement signal using power provided by thecharge storage device in response to the autonomous measurement command;(ii) generate first measurement information based on the first analytemeasurement signal; and (iii) store the first measurement information inthe non-volatile storage medium.

In some embodiments, the sensor may include a clock that is powered bythe charge storage device, and the measurement scheduler may beconfigured to use an output of the clock to determine when to issue themeasurement command. In some embodiments, the sensor may include a powerswitch configured to switch one or more of the sensor elements and themeasurement controller from being powered by the external device tobeing powered by the charge storage device in response to the autonomousmeasurement command.

Another aspect of the invention may provide a method of using a sensorto measure an analyte in a medium within a living animal. The method mayinclude using a charge storage device of the sensor to power ameasurement scheduler. The method may include using the measurementscheduler to issue an autonomous measurement command. The method mayinclude controlling sensor elements of the sensor to generate a firstanalyte measurement signal using power provided by the charge storagedevice in response to the autonomous measurement command. The firstanalyte measurement signal may be based on a detectable propertyexhibited by an analyte indicator of the sensor, and the analyteindicator may be configured to exhibit the detectable property based onthe amount or concentration of the analyte in the medium. The method mayinclude generating first measurement information based on the firstanalyte measurement signal. The method may include storing the firstmeasurement information in a non-volatile storage medium of the sensor.

In some embodiments, the method may include using the charge storagedevice to power a clock. Using the measurement scheduler to issue anautonomous measurement command may include using an output of the clockto determine when to issue the measurement command. In some embodiments,the method may include switching sensor elements of the sensor frombeing powered by an external device to being powered by the chargestorage device in response to the autonomous measurement command.

Further variations encompassed within the systems and methods aredescribed in the detailed description of the invention below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various, non-limiting embodiments ofthe present invention. In the drawings, like reference numbers indicateidentical or functionally similar elements.

FIG. 1 is a schematic view of an analyte monitoring system embodyingaspects of the present invention.

FIGS. 2A-2C illustrate top, side, and perspective views, respectively,of an inductive element, substrate, and charge storage deviceconfiguration embodying aspects of the present invention.

FIG. 3 is a block diagram illustrating the main functional blocks of thecircuitry of an analyte sensor embodying aspects of the presentinvention.

FIGS. 4A and 4B are a block diagram illustrating the functional blocksof circuitry of an analyte sensor embodying aspects of the presentinvention.

FIG. 5 is a block diagram illustrating the functional blocks of some ofthe circuitry mounted on or fabricated in the substrate of the sensoraccording to some embodiments.

FIG. 6 illustrates the layout of a semiconductor substrate embodyingaspects of the present invention.

FIG. 7 is a flow chart illustrating an exemplary sensor control processthat may be performed by an analyte sensor embodying aspects of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view of an analyte monitoring system embodyingaspects of the present invention. As illustrated in FIG. 1, the systemmay include an analyte sensor 100 and an external device 101. In somenon-limiting embodiments, the sensor 100 may be a fully implantableanalyte sensor. The sensor 100 may be implanted in a living animal(e.g., a living human). The sensor 100 may be implanted, for example, ina living animal's arm, wrist, leg, abdomen, peritoneum, intravenously,or other region of the living animal suitable for sensor implantation.For example, in one non-limiting embodiment, the sensor 100 may beimplanted beneath the skin (i.e., in the subcutaneous or peritonealtissues). The sensor 100 may be configured to measure an analyte (e.g.,glucose, oxygen, cardiac markers, low-density lipoprotein (LDL),high-density lipoprotein (HDL), or triglycerides) in a medium (e.g.,interstitial, intravascular, or intraperitoneal fluids) within theliving animal.

The external device 101 may be an electronic device (e.g., a dedicatedmedical device, transceiver, transmitter, smartphone, personal dataassistant, tablet computer, or other handheld communication device) thatcommunicates with the sensor 100 to provide power to the sensor 100and/or receive measurement information (e.g., photodetector and/ortemperature sensor readings) from the sensor 100. In some non-limitingembodiments, the external device 101 may be a handheld device or anon-body/wearable device. For example, in some embodiments where theexternal device 101 is an on-body/wearable device, the external device101 may be held in place by a band (e.g., an armband or wristband)and/or adhesive (e.g., as part of a biocompatible patch), and theexternal device 101 may convey (e.g., periodically, such as every twominutes, and/or upon user initiation) measurement commands (i.e.,requests for measurement information) to the sensor 100. In someembodiments where the external device 101 is a handheld device,positioning (i.e., hovering or swiping/waving/passing) the externaldevice 101 within range over the sensor implant site (i.e., withinproximity of the sensor 100) may cause the external device 101 toautomatically convey a measurement command to the sensor 100 and receivea reading from the sensor 100. In some embodiments, the external device101 may implement a passive telemetry for communicating with theimplantable sensor 100 via an inductive magnetic link for power and/ordata transfer.

In some embodiments, as illustrated in FIG. 1, the external device 101may include an inductive element 103, and the sensor 100 may include aninductive element 114. In some non-limiting embodiments, the inductiveelements 103 and 114 may be, for example, coils. The inductive element103 of the external device 101 and the inductive element 114 of thesensor 100 may be in any configuration that permits adequate fieldstrength to be achieved when the two inductive elements are broughtwithin adequate physical proximity.

The external device 101 may generate an electromagnetic wave orelectrodynamic field (e.g., by using the inductive element 103) toinduce a current in the inductive element 114 of the sensor 100, whichmay be used to power the sensor 100. The external device 101 may alsoconvey data (e.g., commands) to the sensor 100. For example, in anon-limiting embodiment, the external device 101 may convey data bymodulating the electromagnetic wave used to power the sensor 100 (e.g.,by modulating the current flowing through a coil 103 of the externaldevice 101). The modulation in the electromagnetic wave generated by theexternal device 101 may be detected/extracted by the sensor 100.Moreover, the external device 101 may receive data (e.g., measurementinformation) from the sensor 100. For example, in a non-limitingembodiment, the external device 101 may receive data by detectingmodulations in the electromagnetic wave generated by the sensor 100,e.g., by detecting modulations in the current flowing through the coil103 of the external device 101.

In some embodiments, the magnetic external device-sensor link can beconsidered a “weakly coupled transformer” type. In some embodiments, themagnetic external device-sensor link may provide energy and/or a linkfor data transfer using amplitude modulation (AM). Although in someembodiments, data transfer is carried out using AM, in alternativeembodiments, other types of modulation may be used. In some non-limitingembodiments, the analyte monitoring system may use a frequency of 13.56MHz, which can achieve high penetration through the skin and is amedically approved frequency band, for power transfer. However, this isnot required, and, in other embodiments, different frequencies may beused for providing power to and/or communicating with the sensor 100.

In some non-limiting embodiments, as illustrated in FIG. 1, the sensor100 may be encased in a sensor housing 102 (i.e., body, shell, capsule,or encasement), which may be rigid and biocompatible. The sensor 100 mayinclude one or more analyte indicators 106, which may be, for example, apolymer graft coated, diffused, adhered, or embedded on or in at least aportion of the exterior surface of the sensor housing 102. The one ormore analyte indicator 106 (e.g., polymer graft) of the sensor 100 mayinclude indicator molecules 104 (e.g., fluorescent indicator molecules)exhibiting one or more detectable properties (e.g., optical properties)based on the amount or concentration of the analyte in proximity to theanalyte indicator element.

In some embodiments, the sensor 100 may include sensor elements. In somenon-limiting embodiments, the sensor elements may include one or morelight sources 108, one or more photodetectors 224, 226, and/or one ormore temperature transducers 670. In some embodiments, the one or morelight source 108 may emit excitation light 329 over a range ofwavelengths that interact with the indicator molecules 104. In someembodiments, the one or more photodetectors 224, 226 (e.g., photodiodes,phototransistors, photoresistors, or other photosensitive elements) maygenerate a measurement signal that is indicative of the amount of lightreceived by the photodetectors. One or more of the photodetectors (e.g.,photodetector 224) may be sensitive to emission light 331 (e.g.,fluorescent light) emitted by the indicator molecules 104 such that asignal generated by the photodetector (e.g., photodetector 224) inresponse thereto that is indicative of the level of emission light 331of the indicator molecules and, thus, the amount of analyte of interest(e.g., glucose). In some non-limiting embodiments, one or more of thephotodetectors (e.g., photodetector 226) may be sensitive to excitationlight 329 that is reflected from the analyte indicator element 106 asreflection light 333. In some non-limiting embodiments, one or more ofthe photodetectors may be covered by one or more filters that allow onlya certain subset of wavelengths of light to pass through (e.g., a subsetof wavelengths corresponding to emission light 331 or a subset ofwavelengths corresponding to reflection light 333) and reflect theremaining wavelengths.

In some embodiments, as illustrated in FIG. 1, the sensor 100 mayinclude a substrate 116. In some embodiments, the substrate 116 may be acircuit board (e.g., a printed circuit board (PCB) or flexible PCB) onwhich circuit components (e.g., analog and/or digital circuitcomponents) may be mounted or otherwise attached. However, in somealternative embodiments, the substrate 116 may be a semiconductorsubstrate having circuitry fabricated therein (e.g., using acomplimentary metal oxide semiconductor (CMOS) process, an n-typemetal-oxide-semiconductor (NMOS) process, or a p-typemetal-oxide-semiconductor (PMOS) process). The circuitry may includeanalog and/or digital circuitry. Also, in some semiconductor substrateembodiments, in addition to the circuitry fabricated in thesemiconductor substrate, circuitry may be mounted or otherwise attachedto the semiconductor substrate 116. In other words, in somesemiconductor substrate embodiments, a portion or all of the circuitry,which may include discrete circuit elements, an integrated circuit(e.g., an application specific integrated circuit (ASIC)) and/or otherelectronic components (e.g., a non-volatile memory), may be fabricatedin the semiconductor substrate 116 with the remainder of the circuitryis secured to the semiconductor substrate 116, which may providecommunication paths between the various secured components.

In some embodiments, one or more of the sensor housing 102, analyteindicator element 106, indicator molecules 104, light source 108,photodetectors 224, 226, temperature transducer 670, substrate 116, andinductive element 114 of sensor 100 may include some or all of thefeatures described in one or more of U.S. Patent Application PublicationNos. 2013/0211213, 2014/0018644, and 2013/0241745, all of which areincorporated by reference in their entireties. Similarly, the structureand/or function of the sensor 100 and/or external device 101 may be asdescribed in one or more of U.S. Patent Application Publication Nos.2013/0211213, 2014/0018644, and 2013/0241745.

Although in some embodiments, as illustrated in FIG. 1, the sensor 100may be an optical sensor, this is not required, and, in one or morealternative embodiments, sensor 100 may be a different type of analytesensor, such as, for example, a diffusion sensor or a pressure sensor.

In some embodiments, the sensor 100 may include a charge storage device(CSD) 107. In some embodiments, the charge storage device 107 may be arechargeable battery (e.g., a lithium-ion battery). In some embodiments,the charge storage device 107 may be, for example, a battery or acapacitor or a super capacitor. In some non-limiting embodiments, thecharge storage device 107 may last for a year or more, depending ontotal number of recharge cycles (e.g., the battery 107 may drop to 80%of its initial capacity after 500 recharge cycles). In some non-limitingembodiments, the charge storage device 107 may have enough capacity topower the sensor 100 over desired period of time (e.g., one day, oneweek, one month, three months, six months, twelve months, or more). Insome embodiments, the charge storage device 107 may power the sensor 100(e.g., when the sensor 100 is not receiving power from the externaldevice 101). In some embodiments, using power supplied by the chargestorage device 107, the sensor 100 may operate autonomously and take oneor more analyte measurements when the inductive element 114 of thesensor 100 is not coupled with the inductive element 103 of an externaldevice 101 in an electrodynamic field generated by the external device(i.e., even when the inductive element 114 of the sensor 100 is notco-located with the inductive element 103 of an external device 101). Insome embodiments, the sensor 100 may store one or more autonomousanalyte measurements in a memory within the sensor, and the sensor 100may convey one or more of the stored measurements to the external device101 at a later time when the inductive elements 114 and 103 of thesensor 100 and external device 101 are coupled.

In some non-limiting embodiments, the inductive element 114, substrate116, and battery 107 of the sensor 100 may be arranged within the sensorhousing 102 as illustrated in FIGS. 2A, 2B, and 2C, which show top,side, and perspective views, respectively, of the inductive element 114,substrate 116, and charge storage device 107 configuration. In somenon-limiting embodiments, as shown in FIGS. 2A-2C, the inductive element114 may be configured as a coil (e.g., a planar or spiral coil), and thesubstrate 116 and charge storage device 107 may be located side-by-sidewithin the coil. In some embodiments, as shown in FIGS. 2A and 2C, theinductive element 114 may be shaped so as to accommodate the shape ofthe side-by-side substrate 116 and charge storage device 107. In somenon-limiting embodiments, as shown in FIGS. 2A and 2B, the inductiveelement 114, substrate 116, and charge storage device 107 configurationmay have an overall length, width, and height of 0.56, 0.22, and 0.11inches, respectively. However, this is not required, and, in someembodiments, the inductive element 114, substrate 116, and chargestorage device 107 configuration may have different overall dimensions.The inductive element 114, substrate 116, and charge storage device 107configuration may be encased within the sensor housing 102, and the oneor more light sources 108 mounted on or fabricated in the substrate 116may be configured to emit excitation light 329 to one or more one ormore analyte indicators 106 on or in at least a portion of the exteriorsurface of the sensor housing 102 (see, for example, FIG. 1).

FIG. 3 is a block diagram illustrating the main functional blocks of thecircuitry of an analyte sensor embodying aspects of the presentinvention. In some embodiments, as illustrated in FIG. 3, the circuitrymounted on or fabricated in the substrate 116 of the sensor 100 mayinclude one or more of an analog interface 318, a measurement controller320, a command decoder 322, a memory 324, an input/output (I/O) circuit326, a measurement scheduler 328, and a clock 330. In some embodiments,the analog interface 318 may include one or more sensor elements 332mounted on or fabricated in the substrate 116. In some embodiments, thesensor 100 may alternatively or additionally have one or more sensorelements external to the substrate 116 (i.e., sensor elements that thatare neither mounted on nor fabricated in the substrate 166) butelectrically connected to the analog interface 318 via one or morecontacts.

In some embodiments, the I/O circuit 326 may include I/O digitalcircuitry 334 and/or I/O analog circuitry 336. In some embodiments, theinductive element 114 may be electrically connected to the I/O circuit326, which may use current flowing through the inductive element 114 togenerate power for the sensor 100 and to extract data therefrom. The I/Ocircuit 326 may also convey data (e.g., to an external device 101) bymodulating the current the flowing through the inductive element 114. Insome embodiments, the I/O circuit 326 may be electrically connected tothe charge storage device 107 and may use the charge storage device 107to power the sensor 100 (e.g., at times when the sensor 100 is notreceiving power from an external device 101).

In some embodiments, the charge storage device (CSD) 107 may providepower to the clock 330 and to the measurement scheduler 328. TheCSD-powered clock 330 may provide a continuous clock for drivingcircuitry of the sensor 100 even when the sensor 100 is not receivingpower from an external device 101. The measurement scheduler 328 may usethe continuous clock output of the clock 330 to keep track of time andinitiate autonomous, self-powered analyte measurements when appropriate(e.g., at periodic intervals, such as, for example, every minute, everytwo minutes, every 5 minutes, every 10 minutes, every half-hour, everyhour, every two hours, every six hours, every twelve hours, or everyday). The autonomous analyte measurements may be stored in the memory324. In some embodiments, the I/O circuit 326 may convey one or more ofthe stored measurements to the external device 101 at a later time whenan external device 101 is present (i.e., when the inductive elements 114and 103 of the sensor 100 and external device 101 are coupled, and anelectrodynamic field generated by the external device 101 induces acurrent in the inductive element 114 of the sensor 100).

FIGS. 4A and 4B are a block diagram illustrating, in more detail, thefunctional blocks of circuitry mounted on or fabricated in the substrate116 according to some embodiments. In some embodiments, as shown in FIG.4A, the inductive element 114, which may be in the form of a coil, maybe external to the substrate 116 and may be connected to the I/O analogcircuitry 336 through contacts COIL1 and COIL2. In some embodiments, theI/O analog circuitry 336 may include one or more of a capacitor 438,clamp/modulator 440, a rectifier 442, a data extractor 444, a clockextractor 446, a frequency divider 448, a charge pump 450, a charge pumpcontroller 452, and an oscillator 454. In some embodiments, one or moreof the capacitor 438, clamp/modulator 440, rectifier 442, data extractor444, and clock extractor 446 may be connected to the inductive element114 through one or more of contacts COIL1 and COIL2. The rectifier 442may convert an alternating current produced by the inductive element 114to a direct current that may be used to power the sensor 100. Forexample, the direct current may be used to produce one or more voltages,such as, for example, voltages VDDA, which may be used to power theanalog interface 318, and/or VDDD, which may be used to power one ormore of the I/O digital circuit 336, the memory 324, the measurementcontroller 320, the command decoder 322, the measurement scheduler 318,and a test interface 476. In one non-limiting embodiment, the rectifier442 may be a Schottky diode; however, other types of rectifiers may beused in some alternative embodiments. In some embodiments, the dataextractor 444 may extract data from the alternating current produced bythe inductive element 114. In some embodiments, the clock extractor 446may extract a signal having a frequency (e.g., 13.56 MHz) from thealternating current produced by the inductive element 114. In someembodiments, the frequency divider 448 may divide the frequency of thesignal output by the clock extractor 446. For example, in a non-limitingembodiment, the frequency divider 448 may comprise a 4:1 frequencydivider that receives a signal having a frequency (e.g., 13.56 MHz) asan input and outputs a signal having a frequency (e.g., 3.39 MHz) equalto one fourth the frequency of the input signal. In some embodiments,the frequency divider 448 may output either the frequency divided outputof the clock extractor 446 or the output of the oscillator 454 to theI/O digital circuitry 336. In some embodiments, the outputs of rectifier442 may be connected to one or more capacitors 468 (e.g., one or moreregulation capacitors) through contacts VSUP and VSS.

In some embodiments, as shown in FIG. 4A, the I/O analog circuitry 336may include one or more of a tuning capacitor bank 460 and an overtemperature protection circuit 462. In some embodiments, the tuningcapacitor bank 460 may dynamically tune (or detune) an LC tank circuitincluding the inductive element 114 and the capacitor 438 and therebychange a resonant frequency of the LC tank circuit. In some embodiments,the tuning capacitor bank 460 may change the resonant frequency of theLC tank circuit of the sensor 100 to compensate for detuning of anexternal device 101, to compensate for detuning of the sensor 100 causedby the environment in which the sensor 100 is placed (e.g.,patient-dependent detuning), and/or to change the amount of powerdelivered to the sensor 100. In some non-limiting embodiments, thetuning capacitor bank 460 may comprise a varactor diode (i.e., voltagecontrolled capacitor), which may be used to electronically andprogrammatically change the tuning of the sensor 100 (e.g., to optimizethe communications link between the sensor 100 and an external device101). In some non-limiting embodiments, an over-temperature protectioncircuit 462 may control the tuning capacitor bank 460 to detune thesensor 100 and, thereby, reduce amount of power delivered to the sensor100 in the case of excessive heating of the sensor 100 (e.g.,overheating during charging of the charge storage device 107).

In some embodiments, as shown in FIG. 4A, the I/O analog circuitry 336may include one or more of a CSD charger 456, a charge pump 450, and acharge pump controller 452. In some embodiments, the CSD charger 456 maycharge and/or recharge the charge storage device 107 using powersupplied by an external device 101. In some embodiments, the CSD charger456 may provide a variable threshold voltage for different chargestorage device options. In some non-limiting embodiments, the CSDcharger 456 may use a constant current mode of charging to provide fastmethod of charge storage device charging without sacrificing thecapacity and longevity of charge storage device 107. In someembodiments, the charge pump 450 may produce a voltage VLED that is usedto power the one or more light sources 108. In some embodiments, thecharge pump 450 may additionally or alternatively produce a voltage VCPthat is used by the CSD charger 456 to charge the charge storage device107. In some embodiments, the charge pump controller 452 may controlwhether the charge pump 450 produces the voltage VCP used to charge thecharge storage device 107. In some embodiments, control by the chargepump controller 452 may be dependent on the voltage VSUP, which is thevoltage supplied to the sensor 100 via the inductive element 114 andrectifier 442. For instance, in some non-limiting embodiments, thecharge pump controller 452 may control the charge pump to only producethe voltage VCP used to charge the charge storage device 107 only whenan external device 101 is supplying power to the sensor 100 by inducinga current in the inductive element 114, which the I/O analog circuitry336 of the sensor 100 uses to generate the voltage VSUP.

In some embodiments, the I/O analog circuitry 336 may include a clockcontroller 458. The clock controller 458 may reset the measurementscheduler 328.

In some embodiments, as shown in FIG. 4A, the I/O analog circuitry 336may include a power switch 464. The power switch 464 may switch thesensor 100 between CSD power provided by the charge storage device 107and externally supplied power provided by an external device 101 via theinductive element 114 and rectifier 442 of the sensor 100. In somenon-limiting embodiments, the power switch 464 may switch components ofthe sensor 100 from being powered by the voltage VSUP produced by therectifier 442 using a current induced in the inductive element 114 tobeing powered by the voltage VBAT produced by the charge storage device107.

In some embodiments, the power switch 464 may switch the sensor 100 topower itself from the power of the on-board charge storage device 107 inresponse to an autonomous measurement command initiated by themeasurement scheduler 328. For instance, in some embodiments, the sensor100 may be in a sleep mode while the sensor 100 is not receiving powerfrom an external device 101. In the sleep mode, no power would besupplied to one or more of the I/O digital circuitry 336, commanddecoder 322, memory 324, measurement controller 320, and analoginterface 318. However, in the sleep mode, at least the clock 330 andmeasurement scheduler 328 would receive power from the charge storagedevice 107. The measurement scheduler 328 may use the CSD-powered clock330 to determine when to initiate an autonomous measurement. In someembodiments, in response to an autonomous measurement command from themeasurement scheduler 328, the power switch 464 may switch the sensor100 to the power of the charge storage device 107. In some embodiments,one or more of the I/O digital circuitry 336, command decoder 322,memory 324, measurement controller 320, and analog interface 318 wouldthen be powered by the charge storage device 107. In some non-limitingembodiments, when the sensor 100 is switched to the power of the chargestorage device 107, the voltage VBAT (instead of the voltage VSUP) maybe used to produce the voltage (e.g., voltages VDDA, VDDD, and VLED)that powers the sensor 100. In this way, the measurement scheduler 328can wake up the sensor 100 by issuing a measurement command that causesthe power switch 464 to switch the sensor 100 to the power of the chargestorage device 107.

In some embodiments, as shown in FIG. 4A, the I/O analog circuitry 336may include a CSD monitor 466 configured to monitor the voltage VBATproduced by the charge storage device 107 and provide feedback about thecharge level of the charge storage device 107. For instance, in somenon-limiting embodiments, the CSD monitor 466 may indicate whether thevoltage VBAT is sufficient for sensor operation, and the power switch464 may only switch the sensor 100 to CSD power if the CSD monitor 466indicates that the voltage VBAT is sufficient for sensor operation. Insome non-limiting embodiments, the CSD monitor 466 may determine whetherthe voltage VBAT is sufficient for sensor operation by comparing thevoltage VBAT to an operational threshold voltage. In some non-limitingembodiments, the CSD monitor 466 may indicate whether the charge storagedevice 107 is fully charged, and the CSD charger 456 may be configuredto stop charging the charge storage device 107 when the charge storagedevice 107 is fully charged. In some non-limiting embodiments, the CSDmonitor 466 may determine whether the charge storage device 107 is fullycharged by comparing the voltage VBAT to a fully-charged thresholdvoltage. In some non-limiting embodiments, the measurement scheduler 328may adjust the frequency at which autonomous measurements are takenbased on the charge level of the charge storage device 107 as indicatedby the CSD monitor 466. For instance, in one non-limiting embodiment, ifthe CSD monitor 466 indicates that the charge level of the chargestorage device 107 is low, the measurement scheduler 328 may adjust thefrequency at which autonomous measurements are taken.

In some embodiments, as shown in FIG. 4A, an I/O digital circuitry 334may include one or more of a decoder 470, encoder 472, and protocolstate machine 474. The decoder 470 may decode the data extracted by thedata extractor 444 from the alternating current produced by inductiveelement 114. The command decoder 322 may receive the data decoded by thedecoder 322 and may decode commands therefrom. In some non-limitingembodiments, the command decoder 322 may comprise a status register. Insome embodiments, the encoder 472 may receive data from the commanddecoder 322 and encode the data. In some embodiments, the decoder 470and encoder 472 may decode and encode the data in accordance with acommunication protocol (e.g., Manchester or 8B/10B) as specified by aprotocol state machine 474. In some non-limiting embodiments, the I/Odigital circuitry 336 may include two or more sets of encoders anddecoders with each set having its own protocol state machine. In thisway, the sensor 100 may be able to convey and receive information usingmore than one communication protocol.

In some embodiments, as shown in FIG. 4A, the clamp/modulator 440 of theI/O analog circuitry 336 may receive the data encoded by the encoder 472and may modulate the current flowing through the inductive element 114as a function of the encoded data. In this way, the encoded data may beconveyed wirelessly by the inductive element 114 as a modulatedelectromagnetic wave. The conveyed data may be detected by an externalreading device 101 by, for example, measuring the current induced by themodulated electromagnetic wave in a coil of the external reading device.Furthermore, by modulating the current flowing through the inductiveelement 114 as a function of the encoded data, the encoded data may beconveyed wirelessly by the inductive element 114 as a modulatedelectromagnetic wave even while the inductive element 114 is being usedto produce operating power for the sensor 100. In some non-limitingembodiments, the communications received by the inductive element 114and/or the communications conveyed by the inductive element 114 may beradio frequency (RF) communications. Although, in the illustratedembodiments, the sensor 100 includes a single inductive element 114,some alternative embodiments of the sensor 100 may include two or moreinductive elements (e.g., one coil for data conveyance and one coil forpower and data reception).

In some embodiments, the memory 324 may be a nonvolatile storage medium.In some non-limiting embodiments, the memory 324 may be an electricallyerasable programmable read only memory (EEPROM). However, in somealternative embodiments, other types of nonvolatile storage media, suchas flash memory, may be used. In some embodiments, the memory 324 may bea 20 by 1024 bit memory, but this is not required, and, in somealternative embodiments, the memory 324 may be a different size. In somenon-limiting embodiments, the memory 324 may include an address decoder.In some embodiments, the memory 324 may store measurement informationautonomously generated while the sensor 100 is powered from and on-sitecharge storage device (e.g., charge storage device 107) and/ormeasurement information generated in response to a measurement commandreceived from an external device 101 while the sensor 100 is receivingpower from the external device 101. In some embodiments, the memory 324may additionally or alternatively store one or more time-stampsidentifying when the measurement data was generated, sensor calibrationdata, a unique sensor identification, setup information, and/orintegrated circuit calibration data. In some non-limiting embodiments,the unique identification information may, for example, enable fulltraceability of the sensor 100 through its production and subsequentuse. In some embodiments, the memory 324 may receive write data (i.e.,data to be written to the memory 324) from the command decoder 322 andmay supply read data (i.e., data read from the memory 324) to thecommand decoder 322. In some non-limiting embodiments, memory 324 mayhave an integrated charge pump and/or may be connected to an externalcharge pump.

In some embodiments, as shown in FIG. 4B, the analog interface 318 mayinclude a current source 478, one or more light source drivers 480, ananalog to digital converter (ADC) 482, a signal multiplexer (MUX) 484, acomparator 486, one or more photodetectors 488 (e.g., photodetectors 224and 226), and/or one or more temperature transducers 490 and 492. Insome non-limiting embodiments, the comparator 486 may be atransimpedance amplifier (TIA). However, this is not required, and, insome alternative embodiments, the comparator 486 may be a different typeof comparator. In a non-limiting embodiment, one or more of thetemperature transducers 490 and 492 may be a band-gap based temperaturetransducer. However, in some alternative embodiments, different types oftemperature transducers may be used, such as, for example, thermistorsor resistance temperature detectors. In some non-limiting embodiments,the analog interface 318 may include two temperature transducers 490 and492 for high reliability operation and for detection of temperatureerror/failure with higher probability. In some non-limiting embodiments,the second temperature transducer 492 may be a redundant temperaturetransducer that is the same as the first temperature transducer 490 andmay be for temperature plausibility/diagnostic purposes. In someembodiments, the one or more temperature transducers 490 and 492 may befabricated in the substrate 116 or mounted on the semiconductorsubstrate 116. The one or more temperature transducers 490 and 492 mayoutput an analog temperature measurement signal indicative of thetemperature of the sensor 100.

In some embodiments, as shown in FIG. 4B, the one or more photodetectors488 may be fabricated in or mounted on the substrate 116. In someembodiments, the one or more photodetectors 488 may include aphotodetector array including, for example, eight photodetectors. Insome non-limiting embodiments, the one or more photodetectors may beinterdigitated. In some non-limiting embodiments, one or more of thephotodetectors may have optimized ultraviolet sensitivity. In somenon-limiting embodiments having multiple photodetectors, thephotodetectors 488 may be freely allocated as signal photodetectors(e.g., photodetector 224) or as reference photodetectors (e.g.,photodetector 226). In some non-limiting embodiments, one or more of thephotodetectors 488 may be coated with one or more optical filters. Insome embodiments, the substrate 116 may include one or more contacts,such as, for example, contacts PDEXT1, PDEXT2, PDEXT3, and PDEXT4, forelectrically connecting one or more photodetectors that are external tothe substrate 116. The one or more exterior photodetector contacts maybe connected to photodetector input circuitry 494, which may, forexample, amplify the exterior photodetector inputs and/or provide othersignal processing.

In some embodiments, the one or more light source drivers 480 may drivethe one or more light sources 108 using current provided by the currentsource 478. In some embodiments, the one or more light sources 108 ofthe sensor 100 may include a first light source (e.g., a UV lightsource) and a second light source (e.g., a blue light source). In someembodiments, the one or more light source drivers 480 may include afirst light source driver 496 for driving the first light source and asecond light source driver 498 for driving the second light source. Insome embodiments, as illustrated in FIG. 4B, the first and second lightsources may be mounted to the substrate 116 and connected to thesubstrate 116 via contacts LED1C and LED2C. However, this is notrequired, and, in some alternative embodiments, one or more of the firstand second light sources may be fabricated in the substrate 116. In somenon-limiting embodiments, the one or more light source drivers 480 mayinclude one or more exterior light sources drivers 402 and 404 fordriving one or more exterior light sources (i.e., one or more lightsources of the sensor 100 that are not mounted on or fabricated in thesubstrate 116). In some non-limiting embodiments, the one or more lightsources may be powered using a voltage VLED generated using the chargepump 450. In some embodiments, the one or more light source drivers 480may receive a light source selection signal from the measurementcontroller 320 that identifies which of the one or more light sources108 should be driven by the one or more light source drivers 480.

In some embodiments, the current source 478 may receive a signal fromthe measurement controller 320 indicating the light source current atwhich a light source 108 is to be driven, and the current source 478 mayprovide a current accordingly. The one or more light sources 108 mayemit radiation from an emission point in accordance with one or moredrive signals from the one or more light source drivers 480. Theradiation may excite one or more indicator molecules 104 distributed inone or more analyte indicators 106 on at least a portion of the exteriorsurface of the sensor housing 102. The one or more photodetectors 488(e.g., first and second photodetectors 224 and 226) may each output ananalog light measurement signal indicative of the amount of lightreceived by the photodetector. For instance, the first photodetector 224may output a first analog light measurement signal indicative of theamount of light received by the first photodetector 224, and the secondphotodetector 226 may output a first analog light measurement signalindicative of the amount of light received by the second photodetector226.

In some embodiments, as shown in FIG. 4B, the analog interface 318 mayinclude an input multiplexor 406. The input multiplexor 406 may receivethe analog light measurement signals outputted by the one or morephotodetectors 488 and by any external photodetectors. In someembodiments, under the control of the measurement controller 320, theinput multiplexor 406 may select one or two of the analog lightmeasurement signals to pass through to the comparator 486. In someembodiments, the comparator 486 may amplify and/or compare the one ormore analog light measurement signals received from the inputmultiplexor 406. For instance, in some non-limiting embodiments, theinput multiplexor 406 may select the first and second analog lightmeasurement signals from the first and second photodetectors 224 and226, respectively, and output an analog light difference measurementsignal indicative of the difference between the first and second analoglight measurement signals.

In some embodiments, as shown in FIG. 4B, the analog interface 318 mayinclude a sample and hold (S&H) measurement circuit 408. The S&Hmeasurement circuit 408 may receive one or more of the analog lightmeasurement signals or the analog light difference measurement signaland provide a short-term measurement (e.g., a sample of the effectivephoto current shortly after a respective light source 108 has beenswitched off). In some non-limiting embodiments, the analyte monitoringsystem may use this measure to analyze the dynamic phosphorescence ofthe analyte indicator 106 in order to determine aging effects.

In some embodiments, as shown in FIG. 4B, the signal MUX 484 may receiveone or more analog temperature measurement signals from the one or moretemperature transducers 490 and 492, one or more analog lightmeasurement signals from the one or more photodetectors 488 (and/or fromany external photodetectors), an analog light difference measurementsignal from the comparator 486, and/or one or more analog short termmeasurements from the S&H measurement circuit 408. In some embodiments,under the control of the measurement controller 320, the signal MUX 484may select one of the received signals and output the selected signal tothe ADC 482. The ADC 482 may receive the selected analog signal from thesignal MUX 484, convert the received analog signal to a digital signal,and supply the digital signal to the measurement controller 320. In thisway, the ADC 482 may convert the one or more analog temperaturemeasurement signals, the one or more analog light measurement signals,the analog light difference measurement signal, and/or the one or moreanalog short term measurements to one or more digital temperaturemeasurement signals, one or more digital light measurement signals, adigital light difference measurement signal, and/or one or more analogshort term measurements, respectively. In some embodiments, the ADC 482may supply the digital signals, one at a time, to the measurementcontroller 320. In some non-limiting embodiments, the ADC 482 may be a16 bit ADC, and the ADC 482 may have, for example, a 2 ms conversiontime. However, this is not required, and some alternative embodimentsmay use a different ADC.

In some non-limiting embodiments, the circuitry of sensor 100 mayinclude a field strength measurement circuit. In some embodiments, thefield strength measurement circuit may be part of the I/O analogcircuitry 336, I/O digital circuitry 334, or the measurement controller320, or the field strength measurement circuit may be a separatefunctional component. The field strength measurement circuit may measurethe received (i.e., coupled) power (e.g., in mWatts). The field strengthmeasurement circuit of the sensor 100 may produce a coupling valueproportional to the strength of coupling between the inductive element114 of the sensor 100 and an inductive element 103 of an external device101. For example, in non-limiting embodiments, the coupling value may bea current or frequency proportional to the strength of coupling.

In some non-limiting embodiments, as illustrated in FIG. 4A, theclamp/modulator 440 of the I/O analog circuitry 336 acts as the fieldstrength measurement circuit by providing a value (e.g., I_(couple))proportional to the field strength. As illustrated in FIG. 4B, the fieldstrength value I_(couple) may be provided as an input to the signal MUX484 (e.g., via the input MUX 406). When selected, the signal MUX 484 mayoutput the field strength value I_(couple) to the ADC 482. The ADC 482may convert the field strength value I_(couple) received from the signalMUX 484 to a digital field strength value signal and supply the digitalfield strength signal to the measurement controller 320. In this way,the field strength measurement may be made available to the measurementcontroller 320 (e.g., for determining whether the field strength issufficient to carry out a measurement command received from an externaldevice 101 or for use in initiating an analyte measurement commandtrigger based on dynamic field alignment).

In some embodiments, as shown in FIG. 4A, a test interface 476 may bemounted on or fabricated in the substrate 116. In some embodiments, thetest interface 476 may enable wafer-level production testing of thesubstrate 116. In some non-limiting embodiments, the test interface 476may be an SPI-taped interface (i.e., a wireless communicationinterface). In some non-limiting embodiments, the test interface 476 mayreceive signals via one or more contacts and may output signals via oneor more contacts. The test interface 476 may communicate with themeasurement controller 320 via the command decoder 322.

FIG. 5 is a block diagram illustrating the functional blocks of some ofthe circuitry mounted on or fabricated in the substrate 116 according tosome embodiments. In some embodiments, as shown in FIG. 5, one or moreof the command decoder 322, address decoder of the memory 324, and testinterface 476 may be part of the I/O digital circuitry 334.

In some embodiments, as shown in FIG. 5, the measurement scheduler 328may issue an autonomous measurement command to the command decoder 322,which may decode the command and/or send the command to the measurementcontroller 320. The measurement controller 320 may control the sensorelements 332 of the analog interface 318 to perform an autonomousanalyte measurement, and the results of the autonomous analytemeasurement may be stored in the memory 324.

FIG. 6 illustrates the layout of a substrate 116 according to anon-limiting embodiment of the present invention in which the substrate116 is a semiconductor substrate. In some non-limiting embodiments, thesubstrate 116 may have a length of approximately 6010 μm and a width ofapproximately 1610 μm. However, this is not required, and, in somealternative embodiments, the substrate 116 may have a different lengthand/or a different width. In some embodiments, as shown in FIG. 6, eightphotodetectors 488 (e.g., photodetectors 224 and 226) may be fabricatedin the semiconductor substrate 116, and the substrate 116 may have lightsource mounting pads 610 a, 610 b, 612 a, and 612 b for mounting firstand second light sources 108 (e.g., a UV light source and a blue lightsource). However, this is not required, and, in some alternativeembodiments, the substrate 116 may have a different number ofphotodetectors 488 fabricated therein, the photodetectors 488 may bemounted on the substrate 116 instead of fabricated therein, thesubstrate may have a different number of light source mounting pads(e.g., mounting pads for one or three light sources), and/or the lightsources 108 may be fabricated in the substrate 116 instead of mountedthereon. In some non-limiting embodiment, the light source mounting pads610 a, 610 b, 612 a, and 612 b may connect to the anodes and cathodes oflight sources 108 mounted on the substrate 116.

In some non-limiting embodiments, the photodetectors 488 may besymmetrically formed on each side of a center line of the substrate 116.In some embodiments, the light source mounting pads 610 a, 610 b, 612 a,and 612 b may be configured such that the emission points of lightsources 108, when mounted on the light source mounting pads 610 a, 610b, 612 a, and 612 b, are aligned on the center line running between thephotodetectors 488. Similarly, in some embodiments in which the lightsources 108 are fabricated in the substrate 116, the emission points ofthe fabricated light sources 108 are aligned on the center line runningbetween the photodetectors 488. In some embodiments, the fabrication ofsymmetrical photodetectors 488 (i.e., photodetectors 488 which aresymmetrical relative to the light source emission points) may realizedual channels that are closer to being identical to each other than canbe achieved by using discrete parts (e.g., photodetectors mounted on thesemiconductor substrate 116). The nearly identical photodetectorchannels may improve the accuracy of the sensor measurements. This maybe especially true when, in some embodiments, the nearly identical dualphotodetector channels are utilized as a signal channel and a referencechannel, respectively.

In some embodiments, as illustrated in FIG. 6, the photodetectors 488may surround the light source mounting pads 610 a, 610 b, 612 a, and 612b. In some non-limiting embodiments, the photodetectors 488 above andbelow the light source mounting pads 610 a, 610 b, 612 a, and 612 b maybe larger than the photodetectors 488 to the left and right of the lightsource mounting pads 610 a, 610 b, 612 a, and 612 b. However, this isnot required, and, in some alternative embodiments, all of thephotodetectors 488 may have the same size.

The layout of the photodetectors 488 on silicon substrate 116 is notlimited to the embodiment illustrated in FIG. 6. One or more alternativeembodiments may use different photodetector layouts.

FIG. 7 is a flow chart illustrating a non-limiting embodiment of asensor control process that may be performed by the analyte sensor 100.In some embodiments, the sensor control process may begin with a step702 in which the sensor 100 enters a sleep (i.e., dormant) mode. In someembodiments, in the sleep mode, no power is supplied to one or more ofthe I/O digital circuitry 336, command decoder 322, memory 324,measurement controller 320, and analog interface 318, but at least theclock 330 and measurement scheduler 328 are powered by the chargestorage device 107.

In some embodiments, the sensor control process may include a step 704of supplying power to the sensor 100 by coupling the inductive element103 of the external device 101 and the inductive element 114 of thesensor 100 within an electrodynamic field. If power is supplied to thesensor 100 (i.e., if the inductive elements 103 and 114 are coupledwithin an electrodynamic field), the sensor control process may proceedto a step 706. However, if no power (or insufficient power) is suppliedto the sensor 100, the sensor control process may proceed to a step 716.

In some embodiments, the sensor control process may include a step 706of waking-up/activating the sensor 100 using power supplied by anexternal device 101. In some embodiments, the supplied power wake-upstep 706 may include using the electrodynamic field to generateoperational power. In some non-limiting embodiments, the electrodynamicfield may induce a current in inductive element 114 of sensor 100, andthe input/output (I/O) analog circuitry 336 may convert the inducedcurrent into power for operating the sensor 100. In some non-limitingembodiments, the rectifier 442 may convert an alternating currentproduced by the inductive element 114 to a direct current that may beused to power the sensor 100. In some non-limiting embodiments, therectifier 442 may supply a voltage VSUP, and the I/O analog circuitry336 may use the voltage VSUP to produce one or more voltages, such as,for example, voltage VDDA, which may be used to power the analoginterface 318; voltage VLED, which may be used to power the one or morelight sources 108; and voltage VDDD, which may be used to power one ormore of the I/O digital circuit 336, the memory 324, the measurementcontroller 320, the command decoder 322, the measurement scheduler 318,and the test interface 476.

In some embodiments, the sensor control process may include a step 707in which the sensor 100 determines whether a command has been decoded(e.g., from modulation of the electrodynamic field). In somenon-limiting embodiments, the data extractor 444 may extract data fromthe current induced in inductive element 114, the decoder 470 may decodethe extracted data, and the command decoder 322 may decode one or morecommands (e.g., a measurement command) from the decoded extracted data.The command decoder 322 may send a decoded command to the measurementcontroller 320. In some embodiments, the one or more commands and powerreceived by the sensor 100 may be received from the external device 101.

If a measurement command has not been decoded, the sensor controlprocess may return to step 707 until a measurement command is received(assuming power continues to be supplied to the sensor 100). If ameasurement command has been decoded, the sensor control process mayproceed to steps 708, 710, 712, and 714 for execution of the measurementcommand. In some embodiments, the sensor 100 may execute the decodedmeasurement command under control of the measurement controller 320.

In some embodiments, the sensor control process may include a step 708in which the sensor 100 performs a measurement and conversion process.The measurement and conversion process may, for example, be performed bythe analog interface 318 under control of the measurement controller320. In some embodiments, the measurement and conversion sequence mayinclude generating one or more analog measurements (e.g., using one ormore of temperature transducers 488 and 490, one or more of lightsources 108, one or more of photodetectors 480, one or more externalphotodetectors, the S&H measurement circuit 408, and/or comparator 486)and converting the one or more of the analog measurements to one or moredigital measurements (e.g., using ADC 482). One example of themeasurement conversion process that may be performed in step 708 isdescribed with reference to FIG. 18 in U.S. Patent ApplicationPublication No. 2013/0241745, which is incorporated by reference hereinin its entirety.

In some embodiments, the sensor control process may include a step 710in which the sensor 100 may generate measurement information inaccordance with the one or more digital measurements produced during themeasurement and conversion sequence performed in step 708. Depending onthe one or more digital measurements produced in step 710, themeasurement information may be indicative of the amount of an analyte ina medium in which the sensor 100 is implanted. In some embodiments, instep 710, the measurement controller 320 may receive the one or moredigital measurements and generate the measurement information. In someembodiments, the measurement information may include a time-stampidentifying the time at which the analyte measurement was taken.

In some embodiments, the sensor control process may include a step 712in which the sensor 100 stores the measurement information. In someembodiments, the measurement controller 320 may output the analytemeasurement information to the command decoder 322, which may transferthe analyte measurement information to the memory 324. The memory 324may save the received analyte measurement information. In someembodiments, the measurement controller 320 or command decoder 322identify an address at which the measurement information is to be savedin the memory 324. In some non-limiting embodiments, the memory 324 maybe configured as a first-in-first-out (FIFO) or last-in-first-out (LIFO)memory.

In some embodiments, the sensor control process may include a step 714in which the sensor 100 conveys the analyte measurement information. Insome embodiments, the sensor control process may proceed to step 714after storing the measurement information in step 712. However, this isnot required, and, in some alternative embodiments, the sensor controlprocess may proceed to step 714 directly from step 710 in which themeasurement information was generated. In some embodiments, the commanddecoder 322 may transfer the measurement information generated by themeasurement controller 320 to the encoder 472. The encoder 472 mayencode the measurement information. The clamp/modulator 442 may modulatethe current flowing through the inductive element 114 as a function ofthe encoded measurement information. In this way, the encodedmeasurement information may be conveyed wirelessly by the inductiveelement 114 as a modulated electromagnetic wave. In some embodiments,the encoded measurement information wirelessly conveyed by the sensor100 may be received by an external device 101.

In some embodiments, in step 714, the sensor 100 may convey storedmeasurement information generated from one or more previous analytemeasurements in addition to conveying the measurement informationgenerated from the most recent analyte measurement. In some non-limitingembodiments, the sensor 100 may convey stored measurement informationgenerated from a set number (e.g., five, ten, twenty, or one hundred) ofprevious analyte measurements in addition to the most recent analytemeasurement. However, this is not required, and, in some alternativeembodiments, the sensor 100 may convey all of the stored measurementinformation that was generated within a set period of time (e.g., all ofthe stored measurement information that was generated within the lastone minute, five minutes, half hour, hour, four hours, twelve hours,day, or week). In some non-limiting embodiments, the stored measurementinformation may be accessed from the memory 324. In some non-limitingembodiments, the command decoder 322 may transfer the stored measurementinformation retrieved from the memory 324 to the encoder 472. Theencoder 472 may encode the stored measurement information. Theclamp/modulator 442 may modulate the current flowing through theinductive element 114 as a function of the encoded stored measurementinformation. In this way, the encoded stored measurement information maybe conveyed wirelessly by the inductive element 114 as a modulatedelectromagnetic wave. In some embodiments, the encoded storedmeasurement information wirelessly conveyed by the sensor 100 may bereceived by an external device 101. In some embodiments, conveyingmeasurement information from one or more previous analyte readings inaddition to the current reading may enable the external device 101 toproduce analyte trend information.

In some embodiments, the sensor 100 may be capable of executing othercommands received by the sensor 100. For example, if command decoder 322decodes a retrieve stored measurement information command in step 707,the sensor control process may proceed directly to step 714, where thesensor 100 conveys stored measurement information from one or moreprevious analyte measurements without generating a new analytemeasurement. In some non-limiting embodiments, the sensor 100 mayexecute a retrieve stored measurement information command by using theget result command execution process 1900 described with reference toFIG. 19 in U.S. Patent Application Publication No. 2013/0241745, whichis incorporated by reference herein in its entirety.

In some embodiments, the sensor control process may include a step 716in which the sensor 100 determines whether to perform an autonomousmeasurement. In some embodiments, the sensor 100 may perform step 716while the sensor 100 is in sleep mode if no power (or insufficientpower) is supplied to the sensor 100 (see steps 702 and 704). In someembodiments, the CSD-powered measurement scheduler 328 may determinewhether to perform an autonomous measurement based on the continuousclock output of the CSD-powered clock 330. The measurement scheduler 328may use the continuous clock output to keep track of time and may issuean autonomous measurement command when appropriate (e.g., at periodicintervals). If no autonomous measurement command has been issued, thesensor control process may proceed back to step 702. If an autonomousmeasurement command has been issued, the sensor control process mayproceed to step 718.

In some embodiments, the sensor control process may include a step 718of waking-up/activating the sleeping/dormant sensor 100 using powersupplied by the charge storage device 107. In some embodiments, the CSDpower wake-up step 718 may include using the power switch 464 to switchthe sensor 100 from externally supplied power to CSD power. In somenon-limiting embodiments, in response to an autonomous measurementcommand, the power switch 464 may switch components of the sensor 100from being powered by the voltage VSUP produced by the rectifier 442using a current induced in the inductive element 114 to being powered bythe voltage VBAT produced by the charge storage device 107. In someembodiments, after the power switch 464 switches the sensor 100 to CSDpower, one or more of the I/O digital circuitry 336, command decoder322, memory 324, measurement controller 320, and analog interface 318would then be powered by the charge storage device 107.

In some embodiments, after performing the CSD power sensor wake-up instep 718, the sensor control process may proceed to steps 720, 722, and724 for execution of the autonomous measurement command. In someembodiments, in step 720, the sensor 100 may perform a measurement andconversion process. In some embodiments, in step 722, the sensor 100 maygenerate measurement information in accordance with the one or moredigital measurements produced during the measurement and conversionsequence performed in step 720. In some embodiments, in step 724, thesensor 100 may store the measurement information. In some non-limitingembodiments, the steps 720, 722, and 724 may be similar to steps 708,710, and 712, respectively, except that steps 720, 722, and 724 may beperformed with one or more of the I/O digital circuitry 336, commanddecoder 322, memory 324, measurement controller 320, and analoginterface 318 powered by the charge storage device 107 (instead of beingpowered by current induced in the inductive element 114 and rectified bythe rectifier 442).

In some embodiments, after completion of steps 720, 722, and 724, thepower switch 464 may switch the sensor 100 from CSD power to externallysupplied power. If there is no externally supplied power (i.e., if theinductive elements 114 and 103 are not coupled within an electrodynamicfield), the sensor control process may return to sleep mode. In somenon-limiting embodiments, the measurement information stored in step 724during execution of an autonomous measurement command may later beconveyed from the sensor 100 (e.g., in step 714) at a time when theinductive element 114 of the sensor is coupled with the inductiveelement 103 of an external device 101 in an electrodynamic fieldgenerated by the external device 101.

In some embodiments, the sensor 100 may operate in low and high RF fieldsituations while powered by the charge storage device 107. In someembodiments, the low RF field situation occurs when the electrodynamicfield is not strong enough to power a full sensor measurement. In somenon-limiting embodiments, in a low RF field situation, the chargestorage device 107 may power the sensor 100 or supplement the powerprovided by the weak electrodynamic field. In some embodiments, the highRF field situation occurs when the electrodynamic field is strong enoughto power a full sensor measurement. In some non-limiting embodiments, ina high RF field situation, the charge storage device 107 and/or the highRF field may power the sensor 100.

Embodiments of the present invention have been fully described abovewith reference to the drawing figures. Although the invention has beendescribed based upon these preferred embodiments, it would be apparentto those of skill in the art that certain modifications, variations, andalternative constructions could be made to the described embodimentswithin the spirit and scope of the invention. For example, circuitry ofthe sensor 100 may be implemented in hardware, software, or acombination of hardware or software. The software may be implemented ascomputer executable instructions that, when executed by a processor,cause the processor to perform one or more functions.

For another example, in some alternative embodiments, the sensor 100 maynot include a charge storage device 107. In these alternativeembodiments, the sensor 100 may require externally supplied power foroperation (e.g., power from an external device 101 placed in theproximity of the sensor 100 to provide power and data link to the sensor100).

In some alternative embodiments, instead of determining whether ameasurement command has been decoded in step 707, the sensor 100 maydetermine whether the strength of the electrodynamic field received bythe sensor 100 is sufficient or insufficient for the sensor 100 toperform the analyte measurement and conversion, measurement informationgeneration, measurement information storage, and measurement informationconveyance of steps 708, 710, 712, and 714, respectively. If thestrength of the electrodynamic field is sufficient, the sensor controlprocess may proceed to steps 708, 710, 712, and 714. In somenon-limiting embodiments, circuitry of the sensor 100 may produce acoupling value proportional to the strength of the coupling of theinductive element 103 of an external device 101 and the inductiveelement 114 of the sensor 100. In some non-limiting embodiments, theclamp/modulator 440 of the I/O analog circuitry 336 may produce acoupling value (e.g., I_(couple)) proportional to the received fieldstrength based on the current induced in the inductive element 114 bythe electrodynamic field. In one non-limiting embodiment, the couplingvalue proportional to the field strength may be converted (e.g., by ADC664) to a digital coupling value proportional to the received fieldstrength. In some non-limiting embodiments, the sensor 100 may use theanalog and/or digital coupling value to determine whether the strengthof the electrodynamic field received by the sensor 100 is sufficient forthe sensor 100 to perform an analyte measurement. For instance, in onenon-limiting embodiment, the measurement controller 532 may compare thedigital coupling value to an analyte measurement field strengthsufficiency threshold and produce an indication that the strength of theelectrodynamic field received by the sensor is either sufficient orinsufficient for the implanted sensor to perform the analytemeasurement.

In some alternative embodiments, the sensor 100 may perform one or moreof steps 708, 710, 712, and 714 with the sensor operating under chargestorage device power (e.g., if the current induced in the inductiveelement 114 is sufficient for data communication but insufficient toprovide operational power for the sensor 100). In these alternativeembodiments, the sensor 100 may perform a measurement operationinitiated by an external device 101 with operational power for themeasurement operation being provided by the charge storage device 107.

What is claimed is:
 1. A method of using a sensor to measure an analytein a medium within a living animal, the method comprising: controllingthe sensor elements of the sensor to generate a first analytemeasurement signal using power provided by a charge storage device ofthe sensor while an inductive element of the sensor is not in anelectrodynamic field generated by an external device, wherein the sensorelements are configured to generate the first analyte measurement signalbased on a detectable property exhibited by an analyte indicator of thesensor, and the analyte indicator is configured to exhibit thedetectable property based on the amount or concentration of the analytein the medium; generating first measurement information based on thefirst analyte measurement signal; and controlling an input/outputcircuit of the sensor to wirelessly convey the first measurementinformation to the external device via the inductive element while theinductive element is in an electrodynamic field generated by theexternal device.
 2. The method of claim 1, further comprising: storingthe first measurement information in a nonvolatile storage medium of thesensor; controlling the sensor elements to generate a second analytemeasurement signal using power provided by the charge storage devicewhile the inductive element is not in an electrodynamic field generatedby the external device; generating second measurement information basedon the second analyte measurement signal; and controlling theinput/output circuit of the sensor to wirelessly convey the storedsecond measurement information to the external device via the inductiveelement while the inductive element is in an electrodynamic fieldgenerated by the external device.
 3. The method of claim 2, furthercomprising: issuing an autonomous measurement command based on theoutput of a clock that is powered by the charge storage device; andswitching the sensor elements from being powered by externally suppliedpower to being powered by the charge storage device in response to theautonomous measurement command.
 4. A sensor for implantation within aliving animal and measurement of an analyte in a medium within theliving animal, the sensor comprising: an analyte indicator configured toexhibit a detectable property based on the amount or concentration ofthe analyte in the medium; sensor elements configured to generate ananalyte measurement signal based on the detectable property exhibited bythe analyte indicator; a measurement controller; a non-volatile storagemedium; a charge storage device; and a measurement scheduler that ispowered by the charge storage device and is configured to issue anautonomous measurement command; wherein the measurement controller isconfigured to: (i) control the sensor elements to generate a firstanalyte measurement signal using power provided by the charge storagedevice in response to the autonomous measurement command; (ii) generatefirst measurement information based on the first analyte measurementsignal; and (iii) store the first measurement information in thenon-volatile storage medium.
 5. The sensor of claim 4, furthercomprising a clock that is powered by the charge storage device, whereinthe measurement scheduler is configured to use an output of the clock todetermine when to issue the measurement command.
 6. The sensor of claim4, further comprising a power switch configured to switch one or more ofthe sensor elements and the measurement controller from being powered bythe external device to being powered by the charge storage device inresponse to the autonomous measurement command.
 7. A method of using asensor to measure an analyte in a medium within a living animal, themethod comprising: using a charge storage device of the sensor to powera measurement scheduler; using the measurement scheduler to issue anautonomous measurement command; controlling sensor elements of thesensor to generate a first analyte measurement signal using powerprovided by the charge storage device in response to the autonomousmeasurement command, wherein the first analyte measurement signal isbased on a detectable property exhibited by an analyte indicator of thesensor, and the analyte indicator is configured to exhibit thedetectable property based on the amount or concentration of the analytein the medium; generating first measurement information based on thefirst analyte measurement signal; and storing the first measurementinformation in a non-volatile storage medium of the sensor.
 8. Themethod of claim 7, further comprising using the charge storage device topower a clock, wherein using the measurement scheduler to issue anautonomous measurement command comprises using an output of the clock todetermine when to issue the measurement command.
 9. The method of claim7, further comprising switching sensor elements of the sensor from beingpowered by an external device to being powered by the charge storagedevice in response to the autonomous measurement command.